What did you clean it with? I usually hit bare metal with a few shots of brakleen before painting. Obviously never use water. Bare metal forms surface rust very quickly. Even a day or so is enough for it come back. One time I wire wheeled and needle scaled my front axle on my rusty TJ, all the way down to clean bare metal. Took a family trip out of state for 3 days. When I came back the axle had to be wire wheeled again before painting.
You need to topcoat the rust reformer at minimum. Read the instructions on the paint cans. On heavy heavy rust areas I would use Eastwood rust converter, then rust encapsulator, then 2 coats of rustoleum primer and 2 coats of topcoat. For surface rust I skip the first two steps.
You will know if you did a good job or not. On my TJ the areas I paid attention to and worked hard on with prep still look good to this day after daily driving it in the winter salt and rarely washing. The areas I didn't do enough prep work on the rust came back almost immediately within days.
